Wondering when the right moment is to fit windows into your new build? You’re not alone; it’s a common question, and getting it right is essential. Our team at Mumford & Wood is here to guide you through the process.
When constructing a new build property in the UK, the sequence of each phase is crucial to ensure everything runs smoothly and complies with current building standards. A particularly important milestone is the timing of your window installation. Done right, it helps protect the property from weather exposure while keeping the build on track.
With decades of experience supporting developers, architects, and self-builders across the UK, Mumford & Wood offers beautifully crafted timber windows and expert advice to help your build stay efficient, on budget, and true to your design ambitions.
When Is the Best Time to Fit Windows?
In most UK construction projects, windows are typically installed during the second-fix phase. This stage occurs once the building is sealed from the weather, typically after the roof is on and the external walls are completed, but before internal features such as plastering, flooring, and decorating are underway.
Why Is the Second Fix Phase Ideal?
Protection Against the Elements: Fitting windows too early can expose them to the UK's ever-changing weather, increasing the chance of moisture ingress or material degradation. Installing once the shell is complete shields them from unnecessary wear.
Site Security: Leaving valuable items, such as windows, on an open site makes them vulnerable to damage or theft. Delaying installation until security measures such as doors and locks are in place adds peace of mind.
Performance & Compliance: Proper window installation plays a key role in achieving airtightness and thermal efficiency. Performing this step during the second fix ensures that insulation and seals can be applied accurately, a requirement for passing Building Regulations and achieving low U-values.
Avoiding Construction Damage: Busy building sites come with risks. Windows fitted prematurely might suffer scratches, chips, or dust contamination. Waiting until interior work is nearly finished helps preserve their finish and functionality.
Factors That Can Influence Installation Timing
Build Programme & Milestones: No two new builds are the same. While the second fix is the standard window installation point, your project schedule or construction sequencing may require some flexibility. Coordination with your main contractor and suppliers is key.
Weather Disruptions: British weather can be unpredictable. Heavy rain, extreme cold, or high humidity can affect how sealants set or how materials behave. In such cases, holding off for better conditions may prevent issues later.
Energy Testing Requirements: If your project includes airtightness testing, your windows must be in place beforehand. Installing them earlier in the process can help provide more accurate energy performance results and allow time for any remedial sealing work, if needed.
Should You Install Sooner or Later?
Let’s weigh up the trade-offs:
Installing Early (First Fix or Pre-Roof)
- Allows for early airtightness and pressure testing
- May speed up parts of the schedule
- High risk of weather-related damage
- Exposes windows to the rougher phases of site activity
Installing Later (Post-Second Fix or During Interiors)
- Keeps your windows safe from dust and physical damage
- Makes internal access easier for trades on-site
- May create timing clashes with finishing trades
- It could require extra temporary sealing if the building is already enclosed
Final Thoughts
Generally, fitting windows during the second-fix stage, after the structure is weather-tight but before internal finishes begin, is the most effective approach for UK new builds. It helps avoid damage, keeps your project secure, and allows other trades to move forward with minimal disruption.
That said, site-specific conditions, such as tight deadlines, testing phases, or adverse weather, may require a slightly different plan. The key is to stay flexible and plan ahead.
At Mumford & Wood, we’re always on hand to offer guidance. Our experienced team can help you align your window installation with your build schedule for a seamless, stress-free process.
Explore our full collection of timber windows and doors by requesting a Mumford & Wood brochure, or contact our team for a tailored estimate and installation advice.
